The suppression behavior of copper electrodeposition by additives was studied using a microfluidic device. Strong suppression and its cessation due to additive adsorption and deactivation on the plating surface is believed to be crucial for copper bottom-up TSV (Through Silicon Via) filling. Monitoring of additive deactivation is not easy, however, because adsorption generally co-exists with deactivation in the usual experimental environment. In the present study a micro working electrode was prepared on a microchannel wall and electrodeposition was performed, with in-situ microscopic observation. During the electroplating, the supply of the additive was interrupted by switching of the plating solution in the microfluidic device, and deactivation of the additive was observed directly. Three typical suppressing additives were examined; a commercial leveler, which enabled extreme bottom-up, yielded the most rapid deactivation, whereas PEG (Polyethylene Glycol) maintained suppression for a long time after the additive supply had stopped. Optical microscope images revealed the growth of many protrusions after the leveler supply had been interrupted. Moderate agreement between the experimental results and numerical simulations was found, and the additive adsorption-deactivation parameters, k(p) and km, were estimated. (c) The Author(s) 2018. Published by ECS.